And another legal matter we've been following. The utah doctor on trial for the death of his wife found dead in the bathtub. Emotional and dramatic testimony. THREE OF martin MacNeill's own daughters testifying for the prosecution. Aditi roy has the story. Reporter: One by one, martin MacNEILL'S DAUGHTERS FACED THE Man accused of murdering their mother. I knew something bad happened with my dad. And he said, well, girls, you know, I don't know how to tell you this, but your mom's dead. Reporter: Sistersabrina, vanessa and alexis, spoke to jurors on wednesday, about the DAY michele MacNeill died. The former doctor gave his wife a deadly dose of painkillers, then placed her in a tub, when she was recovering from cosmetic surgery investigators say he compelled her to have. My mom was hesitant to get the surgery. She was talking to my dad, saying that maybe we should delay the surgery. He got really angry at my mom and said, no, you cannot do that. If you don't have the surgery now, you're not getting it. Reporter: Macneill says he is innocent. His lawyers argue michele died of a heart condition. BUT PROSECUTORS say MacNeill killed his wife so he could continue an affair with gypsy willis, the woman who became the live-in nanny shortly after michele's death. I was convinced that she wasn't somebody to worry about that my dad might be involved with. Why is that? Because she was nothing like my mom. Reporter: The defense will try to show that alexis changed her stories over the years. You got the phone records that were inconsistent with your memory. And you changed your story to harmonize with the phone records. I think I was getting the times wrong. I know for a fact, this is when I talked with my mom for the last time. Reporter: For "good morning america," aditi roy, abc news, san francisco.

This transcript has been automatically generated and may not be 100% accurate.